It is common practice in the oil and gas industry to "perforate," or make holes in, the casing in a well bore and a producing formation therebehind in order to obtain oil and gas from the well. These perforating operations are most often conducted through the use of a large number of shaped explosive charges which are run into the well bore in perforating guns which maintain the charges in position and also carry a charge initiation system of some sort.
It is common practice in the prior art to assemble the perforating guns close to or at the site of the well to be perforated, which involves placing the charges in brackets or other similar mounting means to properly orient the charges, and running detonating cord or other initiating means to the charges. The mounting means is then inserted in a charge carrier, which comprises a tubular housing having gun ports therein comprising thin-walled areas adjacent the mouths of the shaped charges placed in the carriers The completed assembly of the charges, mounting means, initiating means and housing comprises a perforating gun. When the charges are initiated, the explosive jets pierce the thin-walled areas, the casing, and the producing formation behind the casing.
When more than one perforating gun is to be employed, such as is the case in formations tens or hundreds of feet in thickness, detonating cord, electrical wires or other charge initiating means are strung from one gun to the next throughout the gun string.
Since operations on oil and gas wells may be conducted in remote locations, in extremely bad weather and during all seasons of the year, this prior art approach to assembling a perforating gun from the various components is inconvenient, to say the least. Moreover, if the required number of charges are not present, the operation may be delayed. Such is also the case if it is discovered that the wrong charges have been sent to the well site, charges have been damaged in transit, or are damaged in assembly with the mounting means and/or carrier. Even worse, the use of the wrong charges may not be discovered until after the perforating operation is conducted, and the casing shattered, the formation ruined, or both. Moreover, there is generally not a clean, well-lighted area in which to perform the assembly work, so that the initiating means may not be properly secured to the charges, and connections from one gun to another may be defective. Finally, to assembly hundreds of charges with mounting means, initiating means and housings may take a day or more, which delays the entire producing operation and therefore costs a substantial sum of money.
Over and above the aforementioned disadvantages, however, is the severe safety hazard inherent in assembling the perforating gun components on site and in running a number of guns in tandem, particularly when explosives of high sensitivity, generally called "primary" explosives, are employed in the guns. Primary explosives present a great hazard due to their ease of initiation by fire, electrical or frictional spark, or impact. Moreover, government regulations in most areas of the world make transport of such primary explosives expensive and difficult by restricting the means of transportation which may be employed, as well as severely limiting the quality of explosive which may be transported together. Great property damage, severe personal injury and even death have been caused by premature gun firing while still on the surface at the well site.